In the art of liquid chromatography, more and more devices are being developed that make use of microfabricated separation channels arranged on the surface of a polymer, silicon or glass wafer. Using etching techniques, said microfabricated separation channels usually have a flat-rectangular cross-section, i.e. are much wider than deep or are much deeper than wide.
To perform and detect a liquid chromatographic separation, said microfabricated separation channels are coupled to a sample injector and to a detector device. Traditionally, this coupling is ensured using a cylindrical connection capillary. The technological challenge surfacing here is that the liquid coming from a round tubing with limited diameter should be spread uniformly over the cross-section of said microfabricated separation channel without creating excessive band broadening or axial dispersion. Similarly, it is also important that at the end of the separation channel a distribution zone is arranged to make the transition between the flow in the flat-rectangular separation channel and the circular tubing needed to lead the sample towards an off-chip detector. If performing liquid chromatography, this transition should occur with a minimum of band broadening. One of the general engineering rules that can be used for the design of these flow distribution structures is that they should have a small total volume, for the band broadening or axial dispersion of a device is generally proportional to its volume.
With this in mind, a solution to disperse the liquid across a microchannel proposed in Sant et al. (2006, Reduction of End Effect-Induced Zone Broadening in Field-Flow Fractionation Channels, Anal. Chem., online publication A-H), and making use of a triangular distribution region with an opening angle between 60 and 90 degrees, has the clear drawback that it would occupy a too large volume if the ratio of separation channel width to inlet channel width is large. For example, if the separation channel would be 1 cm wide, the length of the distribution triangle in the case of 90 degree opening angle a would also have to be 1 cm. The continuously bifurcating channel inlet proposed in U.S. Pat. No. 6,156,273 also makes use of such a diverging channel inlet or outlet.
There is a need in the art for providing a device for the distribution of sample and carrier liquid across a micro-fabricated separation channel, which overcomes at least some of the above-indicated drawbacks.